Multiple cell types are involved in the development and maintenance of chronic inflammation. This is also true in inflammatory bowel disease (IBD), where long-standing activation of immune and nonimmune cells results in severe structural and functional abnormalities. Studies performed during the last funding period have defined the phenotypic and functional characteristics of two types of nonimmune intestinal cells, human intestinal fibroblasts (HIF) and microvascular endothelial cells (HIMEC), and assessed their interaction with mucosal immune cells. The results demonstrated that both HIF and HIMEC play an active role in immunity and inflammation through interaction with immune cells and cytokine production. These observations strongly support the concept that immune-nonimmune cell interactions are critically involved in the pathogenesis of IBD. Investigation of genetic, microbial, and immune factors has recently shown the key role of innate immunity in IBD, and that the receptors mediating such innate immune responses are also expressed by nonimmune cells, allowing them to contribute to mucosal immunity and inflammation. This contribution is likely to be enhanced in IBD due to the increased absorption of bacterial products, which can activate HIF and HIMEC expressing Toll- like (TLR) and NOD-like (NLR) receptors, as shown in our preliminary results. Therefore, based on these premises, we propose to test the following central hypothesis: bacterial products can directly activate mesenchymal and endothelial cells and create self-sustaining stimulatory circuits that amplify and prolong gut inflammation. This hypothesis will be tested by investigating: 1) the expression, modulation and functional response of TLRs and NLRs in HIF and HIMEC; 2) the response of HIF and HIMEC to combined microbial and inflammatory stimuli; 3) the effect of bacterial product stimulation on HIF and HIMEC proinflammatory activity; 4) the epigenetic regulation of TLR- and NLR-induced gene expression in HIF and HIMEC. The results will expand knowledge of the mechanisms of chronic gut inflammation and may identify novel pro-inflammatory pathways as potential targets of future therapeutic intervention in IBD.